ASTRONOMY REPORT FOR SCHOOL PURPOSES ONLY.pptx

A scientific study of celestial objects and phenomena. It encompasses the observation, research, and understanding of everything from planets, stars, galaxies, and nebulae to cosmic rays, black holes, and the origins of the universe.

1. UNIT 6: EARTH AS A PLANET ESTEBAN, JERYMAY D.

2. 6.3: EARTH’S ATMOSPHERE 6.4: LIFE, CHEMICAL EVOLUTION AND CLIMATE CHANGE 6.5: COSMIC INFLUENCES ON THE EVOLUTION OF EARTH 6.2: EARTH’S CRUST 6.1: THE GLOBAL PERSPECTIVE

3. The first humans to see Earth as a blue sphere floating in the blackness of space were the astronauts who made the first voyage around the Moon in 1968.

4. 6.1: THE GLOBAL PERSPECTIVE

5. The Global Perspective By the end of this section, you will be able to: Describe the components of Earth’s interior and explain how scientists determined its structure Specify the origin, size, and extent of Earth’s magnetic field

6. The Global Perspective Earth is composed primarily of heavy elements such as iron, silicon, and oxygen—very different from the composition of the Sun and stars, which are dominated by the light elements hydrogen and helium.

7. Earth’s orbit is nearly circular, and Earth is warm enough to support liquid water on its surface. It is the only planet in our solar system that is neither too hot nor too cold, but “just right” for the development of life as we know it.

8. Earth is composed largely of metal and silicate rock. Most of this material is in a solid state, but some of it is hot enough to be molten. The structure of material in Earth’s interior has been probed in considerable detail by measuring the transmission of seismic waves through Earth. EARTH’S INTERIOR

9. Seismic waves that pass through a planet provide scientists with information about its composition and structure. These waves can travel through different layers and along the surface. Earth's interior has distinct layers with varying compositions that seismic studies have revealed.

10. The top layer is the crust, the part of Earth we know best. The largest part of the solid Earth, called the mantle, stretches from the base of the crust downward to a depth of 2900 kilometers. Beginning at a depth of 2900 kilometers, we encounter the dense metallic core of Earth. With a diameter of 7000 kilometers, our core is substantially larger than the entire planet Mercury.

11. The magnetosphere was discovered in 1958 by instruments on the first US Earth satellite, Explorer 1, The regions of high-energy ions in the magnetosphere are often called the Van Allen belts in recognition of the University of Iowa professor who built the scientific instrumentation for Explorer 1. EARTH’S MAGNETIC FIELD

12. This magnetic field is generated by moving material in Earth’s liquid metallic core. As the liquid metal inside Earth circulates, it sets up a circulating electric current. Earth’s magnetosphere extends about 60,000 kilometers, or 10 Earth radii, in the direction of the Sun. EARTH’S MAGNETIC FIELD

13. 6.2: EARTH’S CRUST

14. By the end of this section, you will be able to: Denote the primary types of rock that constitute Earth’s crust Explain the theory of plate tectonics Describe the difference between rift and subduction zones Describe the relationship between fault zones and mountain building Explain the various types of volcanic activity occurring on Earth

15. Igneous rock was the term used for any rock that has cooled from a molten state. All volcanically produced rock is igneous. Sedimentary rocks are made of fragments of igneous rock or the shells of living organisms deposited by wind or water and cemented together without melting. Metamorphic rocks are produced when high temperature or pressure alters igneous or sedimentary rock physically or chemically. EARTH’S CRUST

16. Plate tectonics is a theory that explains how slow motions within the mantle of Earth move large segments of the crust, resulting in a gradual “drifting” of the continents as well as the formation of mountains and other large-scale geological features. Plate tectonics is a concept as basic to geology as evolution by natural selection is to biology or gravity is to understanding the orbits of planets. PLATE TECTONICS

17. Alfred Wegener (1880–1930) Born in Berlin in 1880, Wegener was, from an early age, fascinated by Greenland, the world’s largest island, which he dreamed of exploring. He studied at the universities in Heidelberg, Innsbruck, and Berlin, receiving a doctorate in astronomy by reexamining thirteenth-century astronomical tables.

18. Plates pull apart from each other along rift zones , such as the Mid-Atlantic ridge, driven by upwelling currents in the mantle. Most rift zones, however, are in the oceans. Molten rock rises from below to fill the space between the receding plates When two plates come together, one plate is often forced beneath another in what is called a subduction zone RIFT AND SUBDUCTION ZONES

19. Along much of their length, the crustal plates slide parallel to each other. These plate boundaries are marked by cracks or faults. When two continental masses are moving on a collision course, they push against each other under great pressure. Earth buckles and folds, dragging some rock deep below the surface and raising other folds to heights of many kilometers. This is the way many, but not all, of the mountain ranges on Earth were formed. FAULT ZONES AND MOUNTAIN BUILDINGS

20. Various types of Volcanic Activity The mid ocean ridges , which are long undersea mountain ranges formed by lava rising from Earth’s mantle at plate boundaries. A second major kind of volcanic activity is associated with subduction zones, and volcanoes sometimes also appear in regions where continental plates are colliding. Other volcanic activity occurs above mantle “hot spots”—areas far from plate boundaries where heat is nevertheless rising from the interior of Earth. VOLCANOES

21. 6.3: EARTH’S ATMOSPHERE

22. By the end of this section, you will be able to: Differentiate between Earth’s various atmospheric layers Describe the chemical composition and possible origins of our atmosphere Explain the difference between weather and climate

23. Most of the atmosphere is concentrated near the surface of Earth, within about the bottom 10 kilometers where clouds form and airplanes fly. Within this region—called the troposphere—warm air, heated by the surface, rises and is replaced by descending currents of cooler air; this is an example of convection. EARTH’S ATMOSPHERE

24. Within the troposphere , temperature decreases rapidly with increasing elevation to values near 50 °C below freezing at its upper boundary, where the stratosphere begins. Near the top of the stratosphere is a layer of ozone (O3), a heavy form of oxygen with three atoms per molecule instead of the usual two. Because ozone is a good absorber of ultraviolet light, it protects the surface from some of the Sun’s dangerous ultraviolet radiation, making it possible for life to exist on Earth.

25. Atmospheric Composition and Origin At Earth’s surface, the atmosphere consists of 78% nitrogen (N2), 21% oxygen (O2), and 1% argon ( Ar ), with traces of water vapor (H2O), carbon dioxide (CO2), and other gases. Variable amounts of dust particles and water droplets are also found suspended in the air. Today we see that CO2, H2O, sulfur dioxide (SO2), and other gases are released from deeper within Earth through the action of volcanoes. (For CO2, the primary source today is the burning of fossil fuels, which releases far more CO2thanthat from volcanic eruptions.).

26. Three possibilities exist for the original source of Earth’s atmosphere and oceans: (1) the atmosphere could have been formed with the rest of Earth as it accumulated from debris left over from the formation of the Sun;

27. (2) it could have been released from the interior through volcanic activity , subsequent to the formation of Earth; or (3) it may have been derived from impacts by comets and asteroids from the outer parts of the solar system. Current evidence favors a combination of the interior and impact sources.

28. Weather and Climate All planets with atmospheres have weather, which is the name we give to the circulation of the atmosphere. The energy that powers the weather is derived primarily from the sunlight that heats the surface. Both the rotation of the planet and slower seasonal changes cause variations in the amount of sunlight striking different parts of Earth.

29. Climate is a term used to refer to the effects of the atmosphere that last through decades and centuries. Changes in climate (as opposed to the random variations in weather from one year to the next) are often difficult to detect over short time periods, but as they accumulate, their effect can be devastating

30. Weather refers to a short-term atmospheric conditions while climate is the weather of a specific region averaged over a long period of time. Climate change refers to long-term changes.

31. 6.4: LIFE, CHEMICAL EVOLUTION AND CLIMATE CHANGE

32. By the end of this section, you will be able to: Outline the origins and subsequent diversity of life on Earth Explain the ways that life and geological activity have influenced the evolution of the atmosphere Describe the causes and effects of the atmospheric greenhouse effect and global warming Describe the impact of human activity on our planet’s atmosphere and ecology

33. LIFE, CHEMICAL EVOLUTION, AND CLIMATE CHANGE As far as we know, Earth seems to be the only planet in the solar system with life. The origin and development of life are an important part of our planet’s story. Life arose early in Earth’s history, and living organisms have been interacting with their environment for billions of years. We recognize that life-forms have evolved to adapt to the environment on Earth, and we are now beginning to realize that Earth itself has been changed in important ways by the presence of living matter. The study of the coevolution of life and our planet is one of the subjects of the modern science of astrobiology.

34. THE ORIGIN OF LIFE The record of the birth of life on Earth has been lost in the restless motions of the crust. According to chemical evidence, by the time the oldest surviving rocks were formed about 3.9 billion years ago, life already existed. At 3.5 billion years ago, life had achieved the sophistication to build large colonies called stromatolites, a form so successful that stromatolites still grow on Earth today.

35. The Evolution of the Atmosphere One of the key steps in the evolution of life on Earth was the development of blue-green algae, a very successful life-form that takes in carbon dioxide from the environment and releases oxygen as a waste product. These successful microorganisms proliferated, giving rise to all the lifeforms we call plants. Since the energy for making new plant material from chemical building blocks comes from sunlight, we call the process photosynthesis .

36. As animals evolved in an environment increasingly rich in oxygen, they were able to develop techniques for breathing oxygen directly from the atmosphere. We humans take it for granted that plenty of free oxygen is available in Earth’s atmosphere, and we use it to release energy from the food we take in.

37. Although it may seem funny to think of it this way, we are lifeforms that have evolved to breathe in the waste product of plants. It is plants and related microbes that are the primary producers, using sunlight to create energy-rich “food” for the rest of us.

38. The Greenhouse Effect and Global Warming We have a special interest in the carbon dioxide content of the atmosphere because of the key role this gas plays in retaining heat from the Sun through a process called the greenhouse effect. The light penetrates our atmosphere, is absorbed by the ground, and heats the surface layers. At the temperature of Earth’s surface, that energy is then reemitted as infrared or heat radiation.

39. However, the molecules of our atmosphere, which allow visible light through, are good at absorbing infrared energy. As a result, CO2 (along with methane and water vapor) acts like a blanket, trapping heat in the atmosphere and impeding its flow back to space. To maintain an energy balance, the temperature of the surface and lower atmosphere must increase until the total energy radiated by Earth to space equals the energy received from the Sun. The more CO2 there is in our atmosphere, the higher the temperature at which Earth’s surface reaches a new balance.

40. Human Impacts on Our Planet Earth is so large and has been here for so long that some people have trouble accepting that humans are really changing the planet, its atmosphere, and its climate. They are surprised to learn, for example, that the carbon dioxide released from burning fossil fuels is 100 times greater than that emitted by volcanoes.

41. Early human hunters killed many large mammals and marsupials, early farmers cut down most of the forests, and the Polynesian expansion across the Pacific doomed the population of large birds.

42. An even greater mass extinction is underway as a result of rapid climate change. In recognition of our impact on the environment, scientists have proposed giving a new name to the current epoch, the anthropocine , when human activity started to have a significant global impact. Although not an officially approved name, the concept of “ anthropocine ” is useful for recognizing that we humans now represent the dominant influence on our planet’s atmosphere and ecology, for better or for worse.

43. 6.5: COSMIC INFLUENCES ON THE EVOLUTION OF EARTH

44. By the end of this section, you will be able to: Explain the scarcity of impact craters on Earth compared with other planets and moons Describe the evidence for recent impacts on Earth Detail how a massive impact changed the conditions for life on Earth, leading to the extinction of the dinosaurs Describe how impacts have influenced the evolution of life on Earth Discuss the search for objects that could potentially collide with our planet

45. Where Are the Craters on Earth? In the course of its history, Earth must therefore have been impacted as heavily as the Moon. The difference is that, on Earth, these craters are destroyed by our active geology before they can accumulate. As plate tectonics constantly renews our crust, evidence of past cratering events is slowly erased. Only in the past few decades have geologists succeeded in identifying the eroded remnants of many impact craters (Figure 8.19). Even more recent is our realization that, over the history of Earth, these impacts have had an important influence on the evolution of life

46. Recent Impacts The collision of interplanetary debris with Earth is not a hypothetical idea. Evidence of relatively recent impacts can be found on our planet’s surface. Meteor Crater is one of the few impact features on Earth that remains relatively intact; some older craters are so eroded that only a trained eye can distinguish them. Nevertheless, more than 150 have been identified.

47. Mass Extinction The impact that produced Meteor Crater would have been dramatic indeed to any humans who witnessed it (from a safe distance) since the energy release was equivalent to a 10-megaton nuclear bomb. The best-documented large impact took place 65 million years ago, at the end of what is now called the Cretaceous period of geological history. This time in the history of life on Earth was marked by a mass extinction , in which more than half of the species on our planet died out.

48. The impact that led to the extinction of dinosaurs released energy equivalent to 5 billion Hiroshima-size nuclear bombs and excavated a crater 200 kilometers across and deep enough to penetrate through Earth’s crust. This large crater, named Chicxulub for a small town near its center, has subsequently been buried in sediment, but its outlines can still be identified. Other worldwide effects included large-scale fires (started by the hot, flying debris from the explosion) that destroyed much of the planet’s forests and grasslands, and a long period in which rainwater around the globe was acidic. It was these environmental effects, rather than the explosion itself, that were responsible for the mass extinction, including the demise of the dinosaurs.

49. Impacts and the Evolution of Life It is becoming clear that many—perhaps most—mass extinctions in Earth’s long history resulted from a variety of other causes, but in the case of the dinosaur killer, the cosmic impact certainly played a critical role and may have been the “final straw” in a series of climactic disturbances that resulted in the “great dying.”

50. A catastrophe for one group of living things, however, may create opportunities for another group. Following each mass extinction, there is a sudden evolutionary burst as new species develop to fill the ecological niches opened by the event. We are the lucky beneficiaries of this process. Impacts by comets and asteroids represent the only mechanisms we know of that could cause truly global catastrophes and seriously influence the evolution of life all over the planet. As paleontologist Stephen Jay Gould of Harvard noted, such a perspective changes fundamentally our view of biological evolution.

51. Impacts in Our Future? The impacts by asteroids and comets that have had such a major influence on life are not necessarily a thing of the past. In the full scope of planetary history, 65 million years ago was just yesterday. The fact that our solar system is home to some very large planets in outer orbits may be beneficial to us; the gravitational fields of those planets can be very effective at pulling in cosmic debris and shielding us from larger, more frequent impacts.

52. We cannot make a similar statement about the asteroids that have not yet been discovered, but these will be found and evaluated one by one for their potential hazard. These asteroid surveys are one of the few really life-and-death projects carried out by astronomers, with a potential to help to save our planet from future major impacts.

53. THAT’S ALL, THANK YOU!